The subject invention is directed to the valve art and, more particularly, to an improved ball valve construction.
The invention is particularly suited for use in small size ball valves used in control systems and the like and will be described with reference thereto; however, as will become apparent, the invention is capable of broader application and can be incorporated in ball valves of a variety of sizes used for many different purposes.
In commonly assigned U.S. Pat. No. 4,026,516 there is disclosed a ball valve structure of the type wherein the flow controlling ball is enclosed in a cartridge or capsule of a suitable resilient packing material such as polytetrafluoroethylene or polyethylene. A compressive preloading is applied to the packing material to produce fluid sealing between the ball surface and the inner walls of the valve chamber.
In the noted patent, the compressive preloading is applied through a novel stem packing and guide bushing arrangement. The arrangement includes a cylinder of resilient packing material surrounding the ball operating stem and confined in a packing gland mounted to act against the ball enclosing cartridge. A preload force is applied to the stem packing which is compressed to thereby cause the gland to act against the ball enclosing cartridge with a spring-like biasing action.
The described arrangment is extremely satisfactory under most operating conditions and in most environments. However, when used under conditions of extreme temperature cycling or when subject to conditions which result in high levels of packing wear, the arrangement does not perform as well as would be desirable.